1. Field of the Invention
The present invention relates to the fabrication of integrated circuits. More particularly, the invention relates to a process and apparatus for depositing dielectric layers on a substrate.
2. Background of the Invention
One of the primary steps in the fabrication of modern semiconductor devices is the formation of metal and dielectric films on a substrate by chemical reaction of gases. Such deposition processes are referred to as chemical vapor deposition or CVD. Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film. The high temperatures at which some thermal CVD processes operate can damage device structures having layers previously formed on the substrate. A preferred method of depositing metal and dielectric films at relatively low temperatures is plasma-enhanced CVD (PECVD) techniques such as described in U.S. Pat. No. 5,362,526, entitled xe2x80x9cPlasma-Enhanced CVD Process Using TEOS for Depositing Silicon Oxidexe2x80x9d, which is incorporated by reference herein. Plasma-enhanced CVD techniques promote excitation and/or disassociation of the reactant gases by the application of radio frequency (RF) energy to a reaction zone near the substrate surface, thereby creating a plasma of highly reactive species. The high reactivity of the released species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperaturefor such PECVD processes.
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two year/half-size rule (often called Moore""s Law), which means that the number of devices that will fit on a chip doubles every two years. Today""s fabrication plants are routinely producing devices having 0.35 xcexcm and even 0.1 8 xcexcm feature sizes, and tomorrow""s plants soon will be producing devices having even smaller geometries.
In order to further reduce the size of devices on integrated circuits, it has become necessary to use conductive materials having low resistivity and insulators having low k (dielectric constant less than 4.0) to reduce the capacitive coupling between adjacent metal lines. Liner/barrier layers have been used between the conductive materials and the insulators to prevent diffusion of byproducts such as moisture onto the conductive material as described in International Publication Number WO 94/01885. For example, moisture that can be generated during formation of a low k insulator readily diffuses to the surface of the conductive metal and increases the resistivity of the conductive metal surface. A barrier/liner layer formed from conventional silicon oxide or silicon nitride materials can block the diffusion of the byproducts. However, the barrier/liner layers typically have dielectric constants that are significantly greater than 4.0, and the high dielectric constants result in a combined insulator that does not significantly reduce the dielectric constant.
FIG. 1A illustrates a PECVD process for depositing a barrier/liner layer as described in International Publication Number WO 94/01885. The PECVD process deposits a multi-component dielectric layer wherein a silicon dioxide (SiO2) liner layer 2 is first deposited on a patterned metal layer having metal lines 3 formed on a substrate 4. The liner layer 2 is deposited by a plasma enhanced reaction of silane (SiH4) and nitrous oxide (N2O) at 300xc2x0 C. A self-planarizing low k dielectric layer 5 is then deposited on the liner layer 2 by reaction of a silane compound and a peroxide compound. The self-planarizing layer 5 retains moisture that is removed by annealing. The liner layer 2 is an oxidized silane film that has effective barrier properties when deposited in a manner which provides a dielectric constant of at least 4.5. The dielectric constant of the oxidized silane film can be decreased to about 4.1 by altering process conditions in a manner that decreases moisture barrier properties of the film. Conventional liner layers, such as SiN, have even higher dielectric constants, and the combination of low k dielectric layers with high k dielectric liner layers can provide little or no improvement in the overall stack dielectric constant and capacitive coupling.
As shown in FIG. 1B, WO 94/01885 further describes an optional SiO2 cap layer 6 that is deposited on the low k dielectric layer 5 by the reaction of silane and N2O. The cap layer 6 is also an oxidized silane film that has good barrier properties when deposited in a manner that provides a dielectric constant of about 4.5. Both the liner layer 2 and the cap layer 6 have a dielectric constant greater than 4.5 and the high dielectric constant layers substantially detract from the benefit of the low k dielectric layer 5.
As devices get smaller, liner layers and cap layers having high dielectric constants contribute more to the overall dielectric constant of a multi-component dielectric layer. Furthermore, known low k dielectric materials generally have low oxide content which makes the material inadequate as an etch stop layer during etching of vias and/or interconnects. Silicon nitride has been the etch stop material of choice for making interconnect lines in low k dielectric materials. However, the silicon nitride has a relatively high dielectric constant (dielectric constant of about 7) compared to the surrounding low k dielectric layers. It has also been discovered that the silicon nitride may significantly increase the capacitive coupling between interconnect lines, even when an otherwise low k dielectric material is used as the primary insulator. This may lead to crosstalk and/or resistance-capacitance (RC) delay that degrades the overall performance of the device. Thus, the silicon nitride etch stop layers are typically removed after etching of the underlying dielectric layers.
Ideally, a low k dielectric layer having both good barrier properties for use as a liner layer and sufficient oxide content for use as an etch stop could be identified and deposited in the same chambers as existing low k dielectric materials. Such barrier layers would not increase the overall dielectric constant of the dielectric layers, and such an etch stop layer would not have to be removed after etching the underlying layers.
U.S. Pat. No. 5,554,570 describes barrier layers for use with thermal CVD silicon oxides wherein an organosilane having a C-H group is oxidized instead of silane to increase the density of deposited films and to improve adhesion between the layers. For example, a thermal CVD layer produced from tetraethoxysilane (TEOS) and ozone, may be deposited between PECVD silicon oxide films produced from an organosilane and N2O or O2.
The barrier layers described in the ""570 patent are preferably dense silicon oxide layers having low carbon contents. The dense layers are deposited using 400 W of high frequency RF power although the use of low frequency RF power is asserted to improve film stress. The barrier layers are preferably produced from alkoxysilanes or chlorinated alkylsilanes and N2O to reduce carbon content and increase the density of the layers.
The ""570 patent does not identify process conditions for making barrier layers having low dielectric constants or for making etch stop layers having high oxide contents. The ""570 patent also does not suggest use of the described layers as a barrier layer adjacent a low k dielectric layer or as an etch stop.
There remains a need for dielectric layers having low dielectric constants, good barrier properties, and high oxide content for use as barrier layers or etch stop layers in sub-micron devices.
The present invention provides a method and apparatus for depositing a silicon oxide layer having a low dielectric constant, sufficient oxygen content for use as an etch stop layer, and some hydrogenated or fluorinated carbon content to impart hydrophobic properties. The silicon oxide layer is produced by plasma assisted chemical vapor deposition of an organosilane, an organosiloxane, or combinations thereof, using low RF power levels to generate reactive oxygen atoms. The silicon oxide layers have excellent barrier properties for use as a liner or cap layer adjacent other dielectric layers such as self-planarizing low k dielectric layers. In addition, the silicon oxide layers can be used as an adhesive layer between different layers, or as an intermetal dielectric layer. A preferred silicon oxide layer is produced by reaction of nitrous oxide, N2O, and methylsilane, CH3SiH3, or dimethylsilane, (CH3)2SiH2, and using from about 10 to about 250 W of high frequency RF power. The layers are annealed at low pressure and high temperature to stabilize properties.
The silicon oxide layers of the present invention are most preferably produced using low levels of constant RF power or pulsed levels of RF power at chamber pressures less than about 10 Torr. Pulsed RF power provides high frequency RF power at about 20 to about 250 W during about 10 to about 30% of the duty cycle. Constant RF power provides high frequency RE power at about 10 to about 200 W. Low power deposition preferably occurs at a temperature range from about xe2x88x9220 to about 40 xc2x0 C. At the preferred temperature range, the deposited film is partially polymerized during deposition and polymerization is completed during subsequent curing of the film.
In a preferred embodiment, a silicon oxide layer is deposited on a patterned metal layer by plasma assisted reaction of one or more organosilane and/or organosiloxane compounds and nitrous oxide using low levels of constant RF power. A self-planarizing dielectric layer is then deposited in the same chamber by reaction of a silicon compound such as methysilane or silane and a peroxide compound such as hydrogen peroxide in the absence of RF power. The self-planarizing dielectric layer is optionally capped in the same chamber by further reaction of the organosilane and/or organosiloxane compound and nitrous oxide using low levels of constant RF power. The liner and cap layers provide strength to the self-planarizing dielectric layer during annealing of the self-planarizing dielectric layer. After annealing, the liner and cap layers serve as barriers which protect the self-planarizing dielectric layer.
The silicon oxide of the present invention has further utility as an etch stop material such as in the manufacture of reliable dual damascene structures having reduced capacitive coupling between interconnect lines. In a preferred embodiment, a low k dielectric film, such as an amorphous carbon (xe2x88x9dxe2x88x92C) or amorphous fluorinated carbon (xe2x88x9dxe2x88x92FC) film, is used with the silicon oxide layer. Other low k materials, such as parylene, parylene copolymers, AF4, BCB, or PAE, or high k materials, such as oxynitride and silicon carbide, may also be used with the silicon oxide layer.
A preferred etch stop process sequence comprises forming a dual damascene structure by depositing a first dielectric layer, such as parylene or a fluorinated silicate glass (FSG) layer, on a substrate, depositing the low k dielectric etch stop of the present invention on the first dielectric layer, patterning the etch stop to define the contacts/vias, depositing a second layer of a dielectric, patterning a resist layer on the second layer of dielectric to define one or more interconnects, and etching the interconnects and contacts/vias. The interconnects are etched down to the etch stop, and then the etching continues past the patterned etch stop to define the contacts/vias. Once the dual damascene structure has been formed, a barrier layer is preferably deposited conformally in the structure prior to filling the structure with copper to isolate the copper from other materials, such as silicon. The upper surface is then planarized using chemical mechanical polishing techniques.
The invention further provides an intermetal dielectric material (IMD) comprising the silicon oxide which is deposited on a conventional etch stop such as silicon oxide or silicon nitride. The silicon oxide can also be deposited as a thin adhesive layer.